This invention relates to a variable stage type carburetor and particularly to a variable stage type carburetor which can prevent a lean mixture charge at the time when the associated engine is operated with high load.
A variable stage type carburetor contemplates that the opening area of a venturi portion defined between a vane and the inner wall of an intake passage is varied by the vane operatively connected to a throttle valve via a link mechanism so that the venturi negative pressure is controlled, while a fuel metering area is varied through cooperation of a jet needle connected to the vane with an orifice provided in the venturi wall surface confronting the vane so that an air-fuel ratio is controlled to a given value. This type of carburetor can set the venturi negative pressure at a considerably high value and has an excellent fuel atomizing characteristics.
However, such shortcoming have been encountered that, since the vane and the throttle valve are mechanically associated, if the load acting on the engine becomes greater, then the venturi negative pressure becomes smaller due to low R. P. M. of the engine despite the opening of the throttle valve is large, thereby decreasing the flow rate of fuel with the resulting leaner mixture charge.